Adaptive equalizers, such as fractionally-spaced linear equalizers (FSLEs) or symbol-spaced linear signal equalizers (SSLEs), may be employed to perform equalization of passband discrete signals, for example. FSLEs are described, for example, in Digital Communication, by Lee and Messerschmitt, available from Kluwer Academic Publishers, 1994, herein incorporated by reference. Such adaptive equalizers may be, for example, a component of a receiver for a broadband amplitude and/or phase-modulation-based communications system, such as a digital carrierless AM/PM (CAP) based system. One such application may include use in an asynchronous transfer mode local area network (ATM LAN) or in "fiber-to-the-curb" systems, for example.
One feature of an FSLE for a quadrature amplitude modulation (QAM) or, alternatively, a CAP-based system, for example, is that the FSLE may perform a "blind" start-up, referred to in this context as "blind equalization." More particularly, the FSLE does not need to employ a start-up or training sequence, as may typically be employed for other types of equalizers. Instead, the FSLE filter tap coefficients may be initialized to one out of L possible initial phases, where L is a positive integer greater than one. The FSLE value of L may be obtained as a ratio of the symbol period (T) to the sampling period (T') for the particular FSLE, where T is a multiple of T'.
As is well-known, adaptive equalizers, such as FSLEs or SSLEs, employ significant computational complexity and intensity to recover symbols at the receiving end of a communications system. A source of this computational complexity is related to updating the filter tap coefficients of the adaptive equalizer. A need therefore exists for reducing the computational intensity of the process of updating the filter tap coefficients of an adaptive equalizer.